Optical isolators are used to cut off the backward light caused by reflection to improve the S/N ratio in optical communication utilizing quartz optical fibers and semiconductor lasers at a wavelength of 1.31 micrometers or 1.55 micrometers as a light source. The optical isolators comprise a Faraday rotational element, two polarizers and a magnet, and it is necessary to reduce the size of each element to miniaturize the isolators. It is difficult, however, to miniaturize polarizers while maintaining its extinction ratio and environment resistance. For example, when using a birefringent crystal or light polarizing beam splitter, it is impossible to reduce its thickness less than an effective beam diameter. Further, when using a conventional light polarizing plate of a polymer type in the form of an elongated dichroic dye, it is possible to reduce its thickness but extinction ratio and environment resistance are insufficient.
Polarizing glasses in which metal microparticles having large aspect ratios are aligned are know as the polarizer satisfying the above requirements (see Japanese Patent Publication No. 27406014 (Patent Reference 1)). This polarizing glass comprises geometrically anisotropic metal particles dispersed in an oriented manner in at least one surface layer of a glass base body, wherein said glass base glass is selected from the group consisting of silicate, borate and borosilicate glasses, and the geometrically anisotropic metal particles are metallic copper particles.    [Patent Reference 1] Japanese Patent Publication No. 27406014    [Patent Reference 2] Japanese Patent Publication No. 2849358